1. Field of the Invention
The present invention relates to a wire electric discharge machine including a control means for holding a wire electrode at a desired angle.
2. Description of the Related Art
In a wire electric discharge machine, a reel on which 5 to 15 kg of wire electrode are wound is ordinarily used. The reel is often attached near an upper portion of a column on a machine front surface of the wire electric discharge machine. Japanese Patent Application Laid-Open No. 2010-179377 discloses a technique for automatically measuring a remaining amount of wire remaining on the reel that is mounted in the wire electric discharge machine.
When the wire electrode is continuously fed out from the reel as electric discharge machining progresses, the amount of wire electrode on the reel gradually decreases. When the wire electrode is ultimately drawn out, the weight of the reel (the weight of the reel itself) is about several 100 g. In this way, the weight of the reel when the wire electrode is completely drawn out is several tenths of the initial weight of the reel on which the wire electrode is wound.
Therefore, as shown in FIGS. 1A and 1B, at the start of machining, a column 21 is in a deformed state in a Y-axis direction (left-right direction in the drawing sheet of FIG. 1A) and/or an X-axis direction (left-right direction in the drawing sheet of FIG. 1B), as a result of the weight of a reel 7. As the electric discharge machining progresses, the weight of the reel 7 becomes lighter. Therefore, the deformation in the X-axis direction and/or the Y-axis direction of the column 21 is eliminated.
FIG. 2A is a diagram illustrating a state in which the deformation of the column 21 in the Y-axis direction is eliminated as a result of the weight of the reel 7 in FIG. 1A becoming lighter. FIG. 2B is a diagram illustrating a state in which the deformation of the column 21 in the X-axis direction is eliminated as a result of the weight of the reel 7 in FIG. 1B becoming lighter.
A wire electrode 3 is supported by an upper wire guide 5 and a lower wire guide 6 that are fixed to the column 21. As the electric discharge machining progresses, the remaining amount of the wire decreases and the weight of the reel 7 changes, thereby causing the deformation of the column 21 to change. This change in deformation causes the angle of the wire electrode 3 with respect to a horizontal plane of a table 11 on which a workpiece 4 is placed to change. As a result, machining accuracy of the electric discharge machining decreases.
Therefore, as a measure against the above-described issue, deformation of the column 21 is suppressed by increasing the size of the column 21 and ensuring the rigidity thereof. However, the size of the wire electric discharge machine increases, and the measure is not cost-effective. In addition, a method can also be used in which the reel 7 is attached to a separate wire feeding device that is separated from the main body of the wire electric discharge machine. However, this method is also not cost-effective because the cost of the separate wire feeding device is required. Furthermore, Japanese Patent Application Laid-Open No. 10-263934 proposes a method in which a component supporting the reel 7 is provided from near a base of the column to minimize the effect of the weight of the reel 7. However, this method is also not cost-effective because the component for supporting the reel 7 is required to be added.